This invention relates to a peripheral control processor which primarily controls information flow between a host processor (CPU) and a peripheral unit (i.e. a display unit, printer, disk, tape, communication unit, modem) and is sometimes called an input-output control processor.
A peripheral control processor is generally used in an information processing system or a data communication system to reduce a host processor's burden, and functions to control data transmission. This processor is set up between a host processor and a peripheral unit as an interface adapter, and is connected to each by bus means. A CRT controller, a disk controller, a printer controller, a communication interface controller, etc. are all well known for performing this function. These processors receive a command from a host processor and control the corresponding peripheral units. Some of their principal functions are data transmission, a request for and acknowledgement of data transmission, and informing a host processor and a peripheral unit of the peripheral control processor's internal status. Circuits to perform these functions are integrated on a semiconductor chip and are encapsulated in a package with a plurality of external leads, pins or other connectors through which data or commands are transferred.
Since a peripheral control processor has active control functions as mentioned above, it acts independently from a host processor. That is, a host processor and a peripheral control processor can form a multi-processing system if they are coupled to each other. A peripheral control processor acts as a master processor for a peripheral unit. Therefore, by continuously supplying a control clock signal to a conventional peripheral control processor, it is always kept on an active condition in the same manner as a host processor. However, an effective working period of a peripheral control processor is shorter than that of a host processor. Therefore, a conventional peripheral control processor consumes power unnecessarily while it is idle or in a standby condition because transistor elements on a semiconductor chip turn on and off repeatedly in response to a control clock signal in the idle time or the standby condition. These shortcomings also occur when a chip's internal circuits are constructed by a complementary insulating gate type semiconductor technology.
Further, in a semiconductor device, cost increases in proportion to the number of external leads or pins. Therefore, it is a disadvantage to add special purpose external leads or pins through which to enter control signals to reduce unnecessary power consumption.